<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>template</title>
</head>

<body>
  <script>
    let b1 = 23;
    let b2 = b1;

    b2 += 12;
    console.log('b1', b1, 'b2', b2);

    let arr1 = [1, 2, 3]
    let arr2 = arr1;
    arr2.push(4);
    console.log('arr', arr1, 'arr', arr2);
  </script>
</body>

</html>